...
private void Draw_Image(Graphics gr) {
Path = new GraphicsPath();
// В цикле добавляю отрезки
...
Point[] pnts = {new Point( (int)x1, (int)x2 ),
new Point( (int)x2, (int)y2 )};
Path.StartFigure();
Path.AddLines(pnts);
Path.CloseFigure();
...
// Конец цикла
gr.DrawPath(Pens.Red, Path);
Path.Dispose();
}